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July 22, 2010

Hot. Hotter. Hottest. How's your AC?

Today marks the eighth straight day of 90-degree-plus weather at BWI-Marshall, the fourteenth such day this month and the thirty-sixth so far this year. So how's your AC holding up?

You'd better hope it's in fine shape, because the next few days will be killers. Perhaps literally.

UPDATE 1:00 p.m. Thursday: The Baltimore City Department of Health has declared Code Red Heat Alerts for Friday and Saturday. Cooling centers will be opened across the city. Call 311 for times and locations. At 2 p.m., the NWS issued Heat Advisories for the region from noon to 9 p.m. Friday.

Forecasters out at the NWS forecast office in Sterling are predicting a high today (Thursday) of 93 degrees at BWI-Marshall Airport, and that was the reading at 3:45 p.m. For reference, it was 91 at Tefe, in the Brazilian Amazon. It may not feel as awful here; the air is a bit less humid. But it goes downhill from here.

Friday is expected to reach a high of 96 degrees at the airport as we come under the influence of Heat forecast mapthat Bermuda High in the western Atlantic Ocean. Humidities will rise, pushing heat index readings into the 95 to 105-degree range. There's only a slight chance for a cooling overnight shower before Saturday.

And Saturday will be the worst day of the week (see map). High temperatures at BWI are forecast to push into triple digits for the sixth time this summer, with even less cloud cover for shade than on Friday. Humidities will be high, driving heat index readings into the 100 to 110-degree range. You had your AC system serviced this spring, right? Good.

Watch for heat advisories, Code Red advisories and such. You know the drill by now. Just stay inside or go where it's cool. The jogging, the roofing, the post-hole digging can wait.

Eric the Red, a professional meteorologist from Baltimore who kept us ahead of the bad news during last winter's snowstorms, says it will be a memorable day.

"I am beginning to think Saturday might end up being one of the worst - if not THE worst - day of the summer. Temps will likely exceed 100 degrees yet again, but this time 'round our dew point may very well be in the lower 70s [oppressively humid]."

Eric sent along the temperature forecast map above. "This is NOT the max. temp. forecast, but rather a snapshot," he said. "I suspect the highest readings will be a bit above what the graphic shows. Ouch."

There's more from Eric below. Click on "Continue reading..."

While we're on the subject, BGE today issued (and later recalled) a press release warning customers with central AC that the electric bills they receive in the next few weeks will reflect the extra energy used during the persistent heat of recent weeks. Some bills may double, the utility said. 

The torture continues.

Eric the Red continues: 

"Impressive numbers are rolling in for Saturday's heat potential. 


"Quick Meteo 101:  You may recall me talking during the winter about temperatures aloft... more specifically, at ~ 5,000 ft (850 mb)... and how you need to be below freezing at that level to get snow.  Well, during the summer, you can use the temperature forecast at that level to also get a pretty good idea of what your heating potential is at the surface.  (There's a bit more to it than this... involving dry versus moist adiabatic lapse rates, surface pressure, convective temperatures, mixing ratios, and compressional heating... but I'm assuming you don't really care for that level of detail.  (Or do you?!) )


"Anyway... here are the details:



"For Friday, the models forecast the temperature at ~ 5,000 ft (850 mb) to hit 23°C/73°F.  Mix that air down to the surface, sans clouds, and you have a max temp of 99-101°F  Hmmm.

"For Saturday, the models forecast the temperature at ~ 5,000 ft (850 mb) to hit 25°C/77°F.  Mix that air down to the surface, sans clouds, and you have a max temp of 103-106°F  Double Hmmm.


"The WRF [a forecast model] brings showers into the area on Saturday, which put a lid on the extreme (100+) heat.  But the GFS [another forecast model] is all about 48 hours of humid, hellish, pure sun-shiney fun!  Considering we'll be at a baseball game... I'll go with the GFS.  Another scoorcher.  Upper 90s tomorrow, 100-degree heat a good bet on Saturday (assuming clouds/showers don't enter the picture). Enjoy! - E"


Posted by Frank Roylance at 11:02 AM | | Comments (10)
Categories: Heat waves


Nothing like issuing a press release announcing you'll be robbing your customers in the weeks ahead. PR department working overtime at BGE, I see. I shudder to imagine what my bill will look like for this hellish month.

The wife will be in New York on Saturday, where she will surely fry, so me and the dog will walk in the early morning and then hole up inside the rest of the day...perhaps taking turns sitting in our freezer.

FR: Robbing? If you used the power, seems to me you have to pay for it. There's an "off" switch somewhere. Rates too high? That's a separate issue.

Frank --

I appreciate your work and all of the info you provide. In one area where I'd love some more info, can you fill us in why there seems to be so little forecast data on humidity? Forecasts rarely mention what is expected in the next few days for humidity, but we can get hourly predictions for temperature.

Obviously it would be great to have a prediction for 3 days out for the dewpoint during the heat of the day, but I realize that might be overly ambitious.

At a minimum why can't there be a simple forecast, say on a scale of 1-10, of how humid it's going to be, ranging from say desert-like conditions to Amazon rainforest?

I know you're not the forecaster, but as you know temperature only tells half the story on days like this, and there really ought to be a much greater emphasis on reporting and forecasting humidity levels. If this info appears, it tends to be buried.

Is the issue technology and modelling? Lack of interest by forecasters? Lack of interest in the reporting community? Lack of demand by readers? Any insights would be greatly appreciated.

FR: Not sure why it's not displayed more prominently. Maybe because it's only an issue during very hot days in summer. But there are relative humidity and dew point forecasts out there. The Sun's print edition has the RH forecasts for the day, but none fore the 5-day forecast. Ditto for the online weather page. But the NWS does a nice job with RH and dew points, in graphical form, for seven days out, at
Most important thing to remember: Look for the dew point number. In summer, anything over 65 degrees gets uncomfortable. Over 70 is oppressive.

Does anyone know the record for 90+ days in a year in this area? Just curious. I saw that it said we have had 36 days so far and that just seems crazy by itself considering it's only July 22nd.

FR: We've reported it here. The record for Baltimore is 54 days, in 1988. The WeatherBlog is currently inviting readers to guess the number for 2010. The person coming closest will win some cheap Sun swag. We have 15 contestants so far, with guesses so far from 38 to 65.

Folks it must be said again and again. Get in touch with your old people. Get in touch with your sick friends and family. Call anyone who faces real issues when it gets this hot. Invite them over, stop to take check on them, or just simply ask if they need anything. Friends and family are the best defense against people suffering in this heat.

I want to guess!!! I'm guessing 66 days.

FR: You're in, Josh. Good luck. But what an awful outcome that would be for the rest of us.

Thanks for the reply regarding humidity. I appreciate the link to the NWS graphical forecast. It's pretty scary for the near future.

One thing I'd disagree about is that it's only an issue for hot summer days -- when it's 65 F and the dewpoint is 60, that's a horrible day too.

Again, I know you're not the forecaster or the designer of the Sun's pages, but I think it would be worth keeping in mind when you talk to these people that humidity matters a huge amount whenever you're doing anything outdoors.

In areas like Maryland where you can see big swings in humidity, it would be huge help when people are planning work and recreation to know what's coming. As you know, 93 and dry is far more comfortable when you're mowing the lawn than 83 and muggy.

Thanks again.

FR: I agree. Getting Chicago to make changes on the page is like pulling teeth. But I will try.

Is it fair to compare to the Brazilian Amazon? It's winter there after all...

FR: Of course not. But the fact that we were hotter than the Amazon jungle says a lot about what we're going through. besides, I don't thing equatorial Brazil sees much seasonal temperature change. Maybe a rainy season and a dry season.

I agree with ThaiChicken.

A word of warning about discussing the issue with Chicago, though:

I grew up in NE Indiana (which has very similar [though not identical] weather as compared to Chicago), and the RH level (dew point was not as discussed in the 1960s and early 70s while I lived there) has not been near as important in the MidWest as it is here in Maryland. That is basically because it is rare to have five, six or more consecutive days of 85 degree (let alone 90 degree plus) days combined with RH or dew points at a high level. It happens sometimes, but it is FAR from the norm.

Considering the disparate concerns about weather between the two geographic points, I wish you good luck, Frank, in your 'discussions' with Chicago.

l hope I'm wrong as well.

A BUNCH of air conditioners went out during the heat wave. I heard people complaining all over the place. The humidity is the worst part. Uhg.

FR: Mine included. Repairs underway this morning.

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About Frank Roylance
This site is the Maryland Weather archive. The current Maryland Weather blog can be found here.
Frank Roylance is a reporter for The Baltimore Sun. He came to Baltimore from New Bedford, Mass. in 1980 to join the old Evening Sun. He moved to the morning Sun when the papers merged in 1992, and has spent most of his time since covering science, including astronomy and the weather. One of The Baltimore Sun's first online Web logs, the Weather Blog debuted in October 2004. In June 2006 Frank also began writing comments on local weather and stargazing for The Baltimore Sun's print Weather Page. Frank also answers readers’ weather queries for the newspaper and the blog. Frank Roylance retired in October 2011. Maryland Weather is now being updated by members of The Baltimore Sun staff

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